Fuel cells have been proposed as a power source for electric vehicles and other applications. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied as a fuel to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode of the fuel cell. A plurality of fuel cells is stacked together in fuel cell stacks to form a fuel cell system. The fuel and oxidant are typically stored in large pressurized hollow vessels, such as fuel tanks, disposed on an undercarriage of the vehicle.
The pressurized vessels may be multi-layered and include at least an inner shell and an outer shell. Some inner shells are manufactured using a rotational molding method. The inner shell is formed utilizing the rotational molding method by disposing bosses in a die cavity with a polymer resin, heating the mold while it is rotated causing the resin to melt and coat walls of the die cavity, cooling the die, and removing the molded inner shell. To form the outer shell, the molded inner shell may undergo a filament winding process. The filament winding process often results in the creation of a space between the outer shell and the inner shell of the fuel tank. Gas that diffuses through the inner shell creates gas pockets between the inner shell and the outer shell.
It would be desirable to develop a hollow pressure vessel and method of forming the same having an inner shell, an outer shell, and a diffusion layer disposed therebetween, wherein the diffusion layer facilitates a venting of a fluid that has diffused through the inner shell.